Technical Field
The present invention relates generally to information processing and, in particular, to discovering windows in temporal predicates.
Description of the Related Art
For event processing, it is often useful to specify a collection of events using a temporal predicate. A temporal predicate is a Boolean formula that refers to time (i.e., a Boolean formula with a variable “now”). Given the current time and a set of events that have already occurred, the problem is to compute the set of events that satisfy the temporal predicate. Using a temporal predicate is both powerful (since predicates can be expressive) and intuitive (since Boolean formulas are easy to comprehend). As time progresses, the truth value of the predicate for each individual event may change. The challenge is to efficiently maintain the collection of events that satisfy the predicate.
One prior art approach to event processing involves tracking the truth of predicates for each event separately. However, this approach suffers from drawbacks. For example, whenever time progresses, the system must discover all stored historical events whose truth values have changed. This discovery operation is expensive in terms of, e.g., computational resources.
Another prior art approach to event processing involves an explicitly-specified window. However, this approach also suffers from drawbacks. For example, the use of an explicitly-specified window restricts expressiveness and can make the program less intuitive.